They're armed and dangerous. Two Brazilian species are the world's first known venomous frogs. They have tiny spines on their heads - particularly on their upper lips -that enable them to inject lethal venom into the bloodstream of an assailant. A single gram of venom from Bruno's casque-headed frog (Aparasphenodon brunoi) would be enough to kill 80 people, or 300,000 mice. The frog's venom is 25 times more poisonous by weight than that of a Brazilian pit viper. Venom from Greening's frog {Corythomantis greening, pictured above) is less dangerous, but still twice as potent as a pit viper's (Current Biology, doi.org/6n7).
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